The present invention generally relates to improved LPCVD processing. In particular, the present invention relates to reducing unwanted build-up in LPCVD pump systems thereby permitting temporary process stops without the potential for lock-up and substantially increasing the time intervals between servicing an LPCVD pump system.
Chemical vapor deposition (CVD) involves the formation of a solid film on a substrate by the reaction of vapor phase chemicals that contain the required constituents. The reactant gases are introduced into a reactant chamber and are decomposed and reacted at a heated surface to form the film. CVD techniques are widely employed in the fabrication of semiconductor structures; therefore, CVD techniques are some of the fundamental building blocks in semiconductor processing. Low pressure chemical vapor deposition (LPCVD) techniques involve, as the name implies, low pressures and are advantageous in that films having high purity, excellent uniformity, and conformal step coverage are obtainable. LPCVD techniques are disadvantageous in that high temperatures are typically required.
Another disadvantage associated with LPCVD processes involves the formation of tetraethylorthosilicate (TEOS) or Si(OC2H5)4 films (or silicon dioxide layers made from TEOS starting material). During the LPCVD TEOS film formation process, the starting gas is continuously introduced into the reactor vessel, but a vacuum is continuously drawn from the reactor vessel through a vacuum extraction system connected to thereto, so that a predetermined low pressure is maintained in the reactor vessel to properly control the growth of the TEOS film. In many instances, the starting gas is not completely used in the formation of the TEOS film, and a large part thereof is undesirably pulled from the reactor vessel into the vacuum extraction system. As a result, the pump/vacuum system responsible for the low pressures, such as a mechanical booster pump, a rotary pump, a blower, and other related pump system elements, are damaged by the deposition therein of the starting gas pulled from the reactor vessel. In particular, the starting gas pulled from the reactor vessel is undesirably deposited in the pumps thereby creating an unwanted build-up in an interior of the vacuum extraction system. TEOS byproducts also create an unwanted build-up in an interior of the vacuum extraction system. TEOS material build-up is characterized by a very sticky film. This is problematic because the build-up on internal surfaces of the LPCVD apparatus and particularly on internal movable parts of the pumps requires frequent vigorous cleanings.
Moreover, TEOS is particularly problematic in LPCVD processes because TEOS gas condenses in the vicinity of 35xc2x0 C. Problems ensue when an LPCVD TEOS film formation process is temporarily stopped, such as during evening hours or during a power glitch causing the pump to shut off. In particular, after the LPCVD apparatus is turned off, the apparatus cools down to room temperatures from its high operating temperatures. Since TEOS gas condenses around 35xc2x0 C., TEOS materials build-up on various elements of the LPCVD apparatus including the pump/vacuum system as the temperature of the LPCVD apparatus cools down. Upon turning the LPCVD apparatus back on, blower vains, rotors and other elements of the pump/vacuum system cannot function properly due to the solid build-up of TEOS material. In many instances, within only 30 minutes after stopping and LPCVD TEOS film formation process, TEOS material builds-up so extensively that it is impossible to turn the LPCVD apparatus back on. Although it is sometimes desirable to temporarily interrupt the LPCVD TEOS film formation process in order to make minor process adjustments, such interruptions are avoided due to the possibility that the LPCVD apparatus cannot be turned back on.
Cleaning a pump/vacuum system in an LPCVD TEOS film formation process requires one to disconnect the pump/vacuum system from the LPCVD apparatus, disassemble the pump/vacuum system, clean the individual parts, reassemble the pump/vacuum system, connect the pump/vacuum system back to the LPCVD apparatus, and testing the cleaned system. This cleaning process typically takes three to four days, which is a long period of time to be off-line. Not only is this cleaning process cumbersome, but the LPCVD apparatus is rendered useless during the long cleaning time, thus inhibiting further semiconductor processing.
The present invention provides an improved LPCVD process by enabling the in situ cleaning of the pump/vacuum system of the LPCVD apparatus. The cleaning is in situ in that the LPCVD apparatus is cleaned without having to disconnect and disassemble the pump/vacuum system while running. The present invention also provides methods for minimizing the accumulation of TEOS material in the pump/vacuum system of the LPCVD apparatus. As a result of the present invention, LPCVD processing is capabilities are lengthened, temporary stops in LPCVD processing are facilitated, and cumbersome cleaning of the pump/vacuum system of the LPCVD apparatus is minimized and/or eliminated.
In one embodiment, the present invention relates to a method of cleaning an LPCVD apparatus having TEOS material build-up therein involving contacting the LPCVD apparatus with a composition containing at least one lower alcohol.
In another embodiment, the present invention relates to a method of reducing TEOS material build-up from interior surfaces of a pump/vacuum system of an LPCVD apparatus having a first amount of TEOS material build-up involving contacting the pump/vacuum system of the LPCVD apparatus with a composition containing at least one lower alcohol under a pressure from about 0.001 Torr to about 800 Torr to provide the pump/vacuum system of the LPCVD apparatus having a second amount of TEOS material build-up, wherein the second amount of TEOS material build-up is at least about 75% by weight less than the first amount of TEOS material build-up.
In yet another embodiment, the present invention relates to an LPCVD method involving the steps of depositing TEOS on a first semiconductor substrate in an LPCVD apparatus; removing the first semiconductor substrate from the LPCVD apparatus; injecting a composition containing at least one lower alcohol into the LPCVD apparatus; and depositing TEOS on a second semiconductor substrate in the LPCVD apparatus.
In still yet another embodiment, the present invention relates to a system for cleaning a low pressure chemical vapor deposition apparatus having TEOS material build-up therein, containing a supply of a composition comprising at least one lower alcohol; an injection port for introducing the composition comprising at least one lower alcohol into the low pressure chemical vapor deposition apparatus; and a pump/vacuum system for removing crystallized TEOS material build-up from the low pressure chemical vapor deposition apparatus.